Use dispatch_once for thread safety
Include json-conformance tests to the repo
Update HTTPShortURLLength & HTTPSShortURLLength

Update HTTPShortURLLength & HTTPSShortURLLength ready for upcoming t.co changes.
Merge pull request #4 from ay8s/master

Update HTTPShortURLLength & HTTPSShortURLLength ready for upcoming t.co changes.
Allow '@' in URLs
Update project
Upgraded to the latest conformance suite
Update comformance tests